Oscillators



July 5, 1960 G. D. BRUCE ETAL 2,944,225

OSCILLATORS Original Filed Sept. 30, 1954 I 0 It... 00000.

m FIG. 1

FIG. 2

INVENTORS GEORGE D. BRUCE y ROBERT L EIBSEN ATTORNEY OSCILLATORS George D. Bruce, Poughkeepsie, and Robert L. Eibsen, Hopewell Junction, N.Y., assignors to International Business Machines Corporation, New York, N.Y., a corporation of New York Continuation of abandoned application Ser. No. 459,387, Sept. 30, 1954. This application Feb. 11, 1957, Ser. No. 639,583

7 Claims. (Cl. 331-413) This application is a continuation of our pending application Serial No. 459,387, filed September 30, 1954, entitled Square Wave Generators Using a Junction Transistor," now abandoned.

This invention relates to oscillators, and especially to square wave generators for operating heavy loads at high frequencies, for example, 100 kc.

Modern high speed computers utilize electrical signal pulses to actuate various computing circuits. For accurate handling of signals and for clear distinction from stray magnetic fields, it is desirable'to use square waves. n

In order to secure high speed operation of the computer, it is desirable to use these square waves at frequencies of approximately 100 kc. In order to coordinate all the functions of a computer, it is essential that all the pulses be timed from the same basic generator. Since such computers are tremendously complex, involving thousands of circuits, it is evident that the load on the basic generator in such a computer is great.

It is desirable to use transistors wherever possible in such a computer, because of the low power requirements of transistors as compared to other equivalent devices.

It is an object of the present invention to provide -a square wave generator suitable for supplying heavy loads at frequencies of the order of 100 kc.

Another object of the invention is to provide such a generator which is suitable for use as the basic pulse generator in a high speed computer.

Another object of the invention is to provide a generator of the type described employing transistors.

The foregoing objects are attained in the circuits described herein by connecting two transistors in pushpull, with a positive feed-back for each transistor and negative cross coupling between the two transistors.

The two transistors, shownas PNP junction transistors, supply currents to the opposite halves of a primary winding on an output transformer. A secondary winding of thetransformer is connected to provide feedback potentials to the bases of the two transistors. The secondary winding is connected so that it supplies a positive feedback from the output circuit of each transistor to its input, and also cooperates with the other half of the primary Winding to provide negative cross coupling from the opposite transistor. The primary and secondary windingsare center tapped, the taps being connected through current limiting means including resistor and capacitor and suitable biasing means to the emitters of the transistors.

The circuit operates as a relaxation oscillator. One transistor comes on and the current flow through it increases due to the positive feedback while the current flow through the other is blocked by the negative cross coupling. This continues until the current limiting resistor in the emitter circuit comes into play, whereupon the current flow decreases, the positive feedback effect stops and negative cross-coupling becomes effective to turn the other transistor on.

Other objects and advantages of the invention will be- Patented July 5, 1960 FIGURE 1 The circuit of Figure 1 includes two PNP transistors 1 and 2, having emitter electrodes 1e, and 2e, base electrodes 1b and 2b, and collector electrodes 1c and 2c.

Collector electrodes 10 and 2c are respectively connected to the opposite ends of a primary winding 3 of an output transformer indicated at 4. The .primary winding 3 has center ta-p 5 connected through a biasing battery 6 to ground.

Transformer 4 has a secondary Winding 7 having opposite terminals connected respectively to the bases 1b and 2b and a center tap 8 which is grounded. The primary and secondary windings 3 and 7 are magnetically arranged and electrically connected so that that half of primary winding 3 which is connected in series with collector 10 produces a magnetic flux in the transformer having a direction such that the potential induced by the flux in winding 7 when the current and flux are increasing has the proper polarity, to provide a positive feedback into the base 1b of transistor 1, thereby further increasing the current flow through collector 10. Conversely, when the current and flux are decreasing, the polarity of the induced potential is reversed, so that it tends to decrease the current still more.

A similar relationship exists between that half of primary winding 3 connected in series with collector 2c and the half of secondary winding 7 connected in series with base 2b.

On the other hand, an increasing current flowing through the half of secondary winding 3 connected in series with collector 10 produces a flux which induces, in that half of secondary winding 7 connected in series the base 2b, a potential having a polarity tending to reduce or block the flow of current in transistor 2. Conversely, a decreasing current through collector 10 pro:

duces a potential at base 2b tending to increase the fiow of current in transistor 2. The same is true of the relationship between the current flow through collector 2 c and the potential induced as a result thereof in series with base 1b. This is the negative cross-coupling arrangement referred to above.

Emitters 1e and 2e are connected together through a wire 9. Connected between wire 9 and ground is a variable resistor ltl in series with battery 11. Also connected between wire 9 and ground are a fixed resistor 12 and a parallel capacitor 13.

An output secondary winding 14 is provided on transformer 4, connected to output terminals 15 and 16.

OPERATION-FIGU RE 1 When the circuit of Figure 1 is first energized, both transistors 1 and 2 tend to conduct. By virtue of the negative cross-coupling eifect described above, onetransistor or the other predominates and cuts oii current flow in the other transistor. Assume that the transistor 1 is the predominating transistor and is effective to cut oif the flow in transistor 2. The current flow through transistor 1 then induces a positive fedback potential in secondary winding 7 in a direction to keep the current increasing through collector is. As this current flow increases, the current flow through emitter 1e and resistor 10 likewise increases. The increased potential drop across resistor 10 tends to swing emitter la in a negative direction, which tends to decrease the current flow in transistor 1. Eventuallv anoint isrea hedv where. h effect of, he n g t ve swing of emitter 1e overcomes the effect of the positive feedback through base 1b and the current flow through cc 9r.; l increasin Wh n h hanren the urrent-. increas ng iee ba k int he se i bec m s a current decreasing feedback, and aidsthecurrentlimiting resistor 10 to decrease the current; through colctorche effe t re mn atir n e ult. in quiclcly switching transistor 1, off. When the current flow through collector 1c is decreasing, the potential induced in secondary Winding 7 Supplies 21 Potential to base 2b tending to increase the current through transistor 2. The increasing current flow through transistor 2 tends to reinforcethe positive feedbaclcintobase 2b, thereby turning transistor. 2 on just as. quicklyas transistor. 1 turns off. The cycle of operation. described above. isthen repeated so thattransistor 1 isagain switched-on. The cycle cbntinues: endlessly.

The frequency of operation of thesquare wavegens erator. isdeterminedby the setting of resistor 10.

Resistor 12 serves to shunt part of the current from battery 11 through resistors 10 and 12- to. ground, and thereby to es tablishapositive bias on the emitters efiectiv'eto turnon the transistors. Capacitor 13 acts as a source of stored potential atthe time of switching, and thereby tends-to make theswitching faster, improving the rise times of the transistors.

I It will be recognized that the transformer coupling allows heavy output currents to be carried in the secondary winding 14, and retainsthe impedanceof the output circuit connected to terminals 15 and 16 substantially independent of the internal-impedance of the generator circuit.

1 FIGURE 2 Figure 2 is generally similar to Figurerl, except that thecurrent connections-are somewhat diiferently located, so that the emitters 1e and 2e are grounded and the biasing potentials from battery 11 and resistor 10 are supplied between ground and the bases 1b and2b. The operation of the circuit of Figure 2 is analogous to that of Figure 1. Corresponding elements have been given the same reference numeralsin thetwo figures. It is considered that further description of Figure 2 or its operation is unnecessary.

While 'I have shown PNP transistors, it will be recognized that NPN transistors could beused with equal facility, providedthe necessary. changes are made in the various battery polarities.

The following table shows by way of example particular values for the. potentials of the. various batteries, and for the impedance of the various resistors and capacitors in circuits which have been operated successfully. In some cases, these values arealso shown in the. drawing. These values are set forth by way of. example only, and the invention is not limited to them nor to any of them.

Table 1 Battery 6 8 volts. Resistor 10 50,000 ohms. Battery 11 15 volts. Resistor 12 1,000 ohms. Capacitor 13 0.005 mfd. Winding 3/winding 7 6 to 1 turn ratio.

means, first non-resonant circuit means including the primary winding means and connected, to the output, electrodes, second non-resonant circuit means including the secondary winding means and connected to the input electrodes in a sense so that the transformer means provides regenerative feedbaclgfrqmeach output electrode to the input electrode of its associated transistor and degenerative feedback from each output electrode to the input electrode of the other transistor, said first and second none on ir eans. and aidt a lstormer means ce stituting the only source of signals for. said' input electrodes and cooperating during anincreaseim current'flow at a constant rate through one. of said output electrodes, to produce a constant potential feedback regenerativ'ely to the input electrode associated with said one output electrode and degeneratively to the other input electrode, a source of unidirectional electricalenergy connected between said first circuit means and said common electrodes to p o de e t flow. htoughi a d qu nutelestred in their high mpedan edirwt o s d m ans ef ec e. to im d u n flow. and; e eby o ermi ess id constant rate of increase and saidconstant'potential feedback.

'A eu in quare a ene ato s defi ed, n. claim 1, including a second source of unidirectional elec-' trical energy n imean cnn est nsi e d cond sourc tw nl d omm e ectrod and a inputec rodes to p e u re t f ow throu h. h np t l ro e n, their low impedance direction.

A f e -r nnins qua e, wa en ratqr tined n. claim 1, in which id c r t .fl imit n means emp i es e ner tive ple between 'Sa QE Q mon electrodes and said inputelectrodes.

A unn n q are av e e a o s efinednv claim 1, in which saidcurrent flow limitingmeans corm.

prises a network of three parallel branches connected be; tween said common electrodes and said;input;electrode s, one of said branches comprisingva variable resistor; in series with a second source of unidirectional energy poled to provide current flow through the; input electrodes in their low impedance direction, a second of said branches comprising a second resistor and the. third of said branches comprisinga capacitor.

A eu ns q re Wa e ator omprisin two transistors, each having aninput electrode, an output' e ectrode. and a common elec rod rans o m r ear shavins P y -s conda y. i in s s indin having aicenter tap, firstnon-resonant circuit means-including the primary winding and connectedto theoutput electrodes, second non-resonantcircuit means. including; the secondary winding and connected tothe ,input-elec trodes in a sense so that the transformer-means pi ovides egenerati e feedbac om ach utput electr de-la input electrode of its associated-transistor and degenerative feedback: from each output eleetrodeto the input electrodeof the other transistor, said first andsecondnonresonant circuit means and said transformer means constituting the only source of Signals for said; inputelectrodes, first connecting means between thecenter tap on the primary winding and a cornmon -.junction,-: second connecting means between the center tap, on. the; secondary winding and the common junction third connecting meansbetween the common eleetrodes andzthe common. junction,v one of said first and; second con necting means; comprising a, first source of unidirectional electrical energy of a polarity to proyidecurrent flow through saidoutput electrodes in their-high; impedance directions, and-one of said second, ar1 d -,thir dconnecting means comprising asecond sourceof-nnidireg tional electrical energy of :a polarity to providecurrent; flow through said input-electrodes in their .low,irnpedancedirection s, andmeansrefiective to limit said lash, mentioned current flow,

6. A, free-running squareswave;ge e ators. efined:- in claim, inc,h; ,1 ns third n ng;onr a ditranstemere means, and non-resonant load means connected to said third winding.

7. A free-runing square wave generator, comprising two transistors, each having an input electrode, an output electrode, and a common electrode, transformer means having primary and secondary windings, each winding having a center tap, first non-resonant circuit means including the primary winding and connected to the output electrodes, second non-resonant circuit means including the secondary Winding and connected to the input electrodes in a sense so that the transformer means provides regenerative feedback from each output electrode to the input electrode of its associated transistor and degenerative feedback from each output electrode to the input electrode of the other transistor, said first and second non-resonant circuit means and said transformer means constituting the only source of signals for said input electrodes, first connecting means between the center tap on the primary winding and a common junction, second connecting means between the center tap on the secondary winding and the common 6 junction, third connecting means between the common electrodes and the common junction, one of said first and second connecting means comprising a first source of unidirectional electrical energy of a polarity to provide current flow through said output electrodes in their high impedance directions, and one of said second and third connecting means comprising first and second parallel branches, said first parallel branch including a variable resistor and said second parallel branch including a capacitor.

References Cited in the file of this patent UNITED STATES PATENTS Kretzmer, presented September 1953, published in Proc. of the I.R.E., vol. 42, pp. 391-401, February 1954. 

